The invention concerns a rotor for an axial flow rotary separator of the type in which crop material engaging elements of the rotor periodically engage material and propel it in a spiral path within a generally cylindrical casing and, particularly, the arrangement of the crop material engaging elements of the rotor.
It is convenient in this context to refer to individual crop material engaging elements as fingers. Successful function requires only that the elements, finger-like, periodically penetrate and withdraw from the crop material mat. Clearly, this requirement may be met by other forms than the simple round rods disclosed by Witzel (U.S. Pat. No. 4,408,618) and in the present application. For example, elements may be tapered, of various cross-sectional shapes, or bifurcated.
Witzel has disclosed a number of rotors for an axial flow rotary separator in which fingers of the rotor each engage the crop material only intermittently but, while in engagement, propel it axially downstream as well as circumferentially. All of the rotors disclosed by Witzel are relatively complex. The simplest embodiment suggested by his disclosure may be described with reference to his FIG. 5. The rotor consists of a bank of finger wheels, each with several fingers, carried on a common fixed shaft, eccentric with respect to the separator casing. The finger wheels are rotatably driven by a surrounding cage or drum concentric with the separator casing. The planes of rotation of the finger wheels are parallel to each other but inclined with respect to the separator casing axis.
One disadvantage of having several circumferentially spaced fingers on a single finger wheel is that, even though they are circumferentially spaced, each finger follows essentially the same oblique path with respect to the casing. Material handling and separating function may be improved by a more dispersed finger pattern but the opportunities of achieving this, for example by relative axial offset between the circumferentially spaced fingers on a single wheel, are limited. And when, as suggested by Witzel, a cage or drum is used, to provide rotational drive for the finger wheels and also provide surfaces contributing to material control and facilitating positive retraction of fingers from the crop material mat, further disadvantages are inherent in the configuration. Because of the eccentricity between finger wheel and drum or cage, the rotational speed of the finger wheel, driven by the drum, is non-uniform constantly accelerating and decelerating even though the drum is driven at constant speed. And the geometry is such that relatively wide slots must be provided in the drum to accommodate the relative displacement, in a circumferential direction, between the fingers and the sides of the drum slots. Wide slots in the drum provide more opportunity for crop material to find its way inside the drum, possibly upsetting rotational balance or causing blockages through wrapping the finger wheel assemblies. Further, the constant transfer of the actual propulsion of the finger wheel from one finger to the next as the rotor rotates, may result in undesirable noise, wear and vibration.